1. Field of the Invention
This invention relates to an exhaust gas purification apparatus, having a particulate filter, for an internal combustion engine. More particularly, the invention relates to an abnormality detection apparatus for detecting an abnormality in an exhaust gas purification apparatus for an internal combustion engine.
2. Description of the Related Art
Reduction of exhaust gas emission has been required in recent years for internal combustion engines mounted in automobiles and so forth. In a compression ignition type Diesel engine using light oil as fuel, in particular, removal of particulate matters such as soot and SOF (soluble organic fraction) in the exhaust gas has been necessary in addition to removal of CO, HC and NOx. Therefore, it has been customary to arrange a particulate filter in an exhaust passage and to trap particulate matters in the exhaust gas.
The particulate filter allows the passage of an inflowing exhaust gas through a porous partition wall and traps, thereby, the particulate matters in the exhaust gas on the surface of the partition wall and the pores. When an amount of the particulate matters so collected becomes excessively great, a back pressure on the internal combustion engine rises due to the increase in the flow resistance in the particular filter and the increase of the back pressure invites a drop in the output. Therefore, it is necessary to appropriately remove the particulate matters accumulated on the particulate filter, to regenerate the particulate filter and to recover the flow capacity of the particulate filter.
A particulate filter that makes it possible to regenerate during the operation of the internal combustion engine includes the one that includes an oxide catalyst such as platinum. This filter supplies fuel to the particulate filter by means of post-injection for injecting the fuel in the exhaust stroke, and oxidizes and removes the accumulated particulate matters that are not easily oxidized in comparison with fuel injection by utilizing the combustion heat.
The fuel consumption is deteriorated when regeneration of the particulate filter is done frequently. When the interval to the next regeneration is too long, on the other hand, the amount of the particulate matters becomes excessively great at the time of the start of regeneration and the accumulated particulate matters are rapidly burnt in the regeneration processing. The particulate filter reaches an abnormally high temperature, and is likely to be broken, in this case. It is therefore desirable to detect the deposition condition of the particulate matters and to decide the regeneration timing of the particulate filter. Japanese Unexamined Patent Publication Nos. 2003-279191 and 2003-83035 disclose a technology that detects a pressure difference by utilizing the phenomenon that the pressure difference between an inlet and an outlet of the particulate filter increases due to the flow resistance resulting from the increase of the amount of the particulate matters described above, and determines the regeneration timing when the pressure difference detected exceeds a predetermined value.
A pressure sensor for detecting the differential pressure is connected to a pressure introduction piping between upstream and downstream sides of the exhaust passage while interposing the particulate filter. This piping is generally a heat-resistant metal pipe or rubber hose. When breakage such as a crack, fall-off, clogging, etc, of the piping occurs depending on the use condition, detection accuracy of the pressure difference drops and the amount of the particulate matters cannot be known. The exhaust gas may leak to the outside when the piping is broken or falls off.